For the Mark Audio speakers in parallel, I set each Proprius to 9 o'clock, 12 o'clock or somewhere inbetween. For a fully opened out K1000, I set the Proprius pots to somewhere before the 3 o'clock position so that I can't hear any hiss. I tend to just set both halfway, at 12 o'clock so that hiss is so low level that I cannot hear it.

For HD540II from Proprius, I think I set the pots at 9-12 o'clock so I couldn't hear hiss. For the more sensitive HD800, I set them at no higher than 9 o'clock. The negative leads were connected common ground. 

Where I set them depends on the load impedance and sensitivity but I never set them out of circuit as my ears can easily pick up low level hiss (you probably already know that I listen carefully and attentively).

For high impedance headphones such as the Sennheisers that I have tested, the Proprius with pots turned down seem equally capable as the Solo ULDE, in my honest opinion. I didn't need series resistors when the pot itself is one big variable resistor. Set the pots fully down before commencing playback then carefully nudge them up a bit, staying under 9 o'clock. At least make sure the pots lie above the slight channel imbalance position at around 7 o'clock so that you're beyond the point where the left channel is slightly louder than the right channel, to where they fully equalise.

HD250II is good but K1000 would show your ears the full extent of how good the Proprius can perform.

I believe the answer is not quite as good...

Why do you think I was happy enough to sell the Solo ULDE originally and just keep the monoblocks for my headphones? Very close, they are. I only bought another Solo UL some time later because I was trying to cost-cut my system and see if I could get everything I wanted out of the headamp. But I had to put both the dials right up when using the Maj-Solo into K1000, to the point where noise/distortion was being reached and the dynamic range reached compression, as though I'd reached a limit of useful gain or ran out of current allowance.

Graham Slee wrote: ] But, as I keep trying to educate this world, electronics isn't perfect - most people mistakenly think it is - but it is man-made from the very stuff we walk upon (rocks and clay). There are trade-offs, and in this example it's hiss. As I've been saying since the very start, low-noise = boredom. Musical fun comes from timing, and timing requires fast electronics, and fast electronics has large slew-rates, and anything having a large slew-rate isn't low noise (as all the data sheets say).

I too am looking forward to the integrated amp as it will suit my needs perfectly.

 

The more sensitive the drivers or the lower their impedance, I am under the impression that amplification noise is more easily heard. I've only used 300 Ohm Sennheisers and 120 Ohm K1000 with them though. I'd imagine that even at lowest pot positions on the Proprius, it would still be unsuitable for devices like IEMs (In-Ear Monitors)

 

I'd guess that less sensitive loads would be driven as well from Proprius as they are from Solo. Some devices may ideally require the extra current that the Proprius can supply.

I'd like to try something similar into my HD600s.

My Proprius are due to arrive in a couple of weeks.

Sounds like some DIY is in order before spending on a posher cable if I like what I hear.

As the Proprius has a label on it saying up to 32 ohms can I just check that I won't invalidate my warranty by using them with higher impedence headphones.

Given your positive involvement in this thread I'm guessing that's not a problem.

As for connecting the grounds of two mono amplifiers, as required to connect headphones, which have a common return - well, it can cause stereo distortion. Stereo ground loop distortion is mainly unknown. You might expect things like that would be important, especially for stereo... and multichannel stuff, but closed minds seem to exist in the magical world of hi-fi.

As John informs me, you will use 300-ohm phones; the current trying to go both ways is far less than you'd have on speakers - nearer to valve amplifier current, and stereo ground loop distortion was only discovered with the arrival of transistors - so might go completely unnoticed.

One might ask if there's a spec for stereo ground loop distortion, and the answer is no, and because of that, it can't exist.

Also, the star earth (discovered by Decca) rendered it inoperable but did it because star earths make rail decoupling impossible unless decoupled to each leg of the star, which voids the star earth, causing stereo ground loop distortion.

Have fun!

Graham 

The nominal impedance of the attached load. (Ohms)

The electrical sensitivity of the attached load (dB SPL per milliwatt)

The dial position of the Proprius (higher positions can produce more noise so choose a position that makes the low-level hiss inaudible)

Proximity of the drivers to the ears (the closer they are, the less power required and the easier it is to hear hiss). This is only relevant with earspeakers and speakers as most headphones have close proximity by design.

Many headphones have removable cables so you can source/make a high quality 4-pin cable if you don't want to use them common ground with the negative terminals joined. But if impedances are high and current flows/oscillations are low, I'm not sure it will matter. I remember the HD800 was clear at 8 o'clock but the sensitivity is too high to use a much higher position without a high noise floor. At about 9 o'clock, noise was creeping in. To use a greater dial range there, a potential divider circuit would have to be implemented to adjust the impedance and tap off voltage.

If you don't mind cutting off the audio jack from the end of the headphone cable, which I believe is where the negative connections will usually join together, they can be separated from each other and connected to separate monoblocks. Not too much of a big deal if the headphone cable is removable and can be replaced with an official spare part.

I tried using the Proprius amps to power my LCD-2 headphones and it was very good. The common ground was fine, I did try splitting it the 4 wire way but couldn't hear a difference. I went back to powering my floorstanding speakers but I definitely support what Ash and Graham have written above.